1. Field of the Invention
The present invention relates to flywheels and, more particularly, to a flywheel that can change vibrational behavior between two kinds of characteristics, thereby suppressing resonance and improving torque variation absorbing effects.
2. Description of the Related Art
Flywheels which comprise driving and driven side flywheels, a spring mechanism for connecting the driving and driven side flywheels, and a friction mechanism are well known, as shown, for example, in U.S. Pat. Nos. 4,468,207, 4,274,524, 4,351,168, 2,042,570, 4,445,876, 2,729,079, 2,437,537, 4,663,983, 4,220,233, 4,002,043; GB-A-2,000,257; DE-A-2,926,012; Automotive Engineering, vol. 93, page 85; Japanese Utility Model Publications SHO 61-23542, SHO 61-23543, SHO 61-23544, SHO 59-113548, SHO 59-108848, SHO 56-6676, and SHO 56-109635; and Japanese Patent Publications SHO 61-59040, SHO 61-59042, and SHO 61-52423; Shock and Vibration Hand Book, Vol. 2, McGraw Hill is useful in understanding the operation of an elastically connected Coulomb damper although it does not relate to flywheels.
The prior art flywheels have a single kind of vibrational characteristic generated by a single kind of spring mechanism, even if the spring mechanism itself includes a plurality of coil springs arranged in series or in parallel with each other. The single kind of vibrational characteristic causes the flywheel to have a single first mode resonance speed throughout the entire range of engine speeds. The resonance speed is usually set lower than the idling speed of the engine. As a result, when the engine speed passes through the resonance speed during a start-up or stopping of the engine, the torsional vibration of the flywheel will be amplified. To suppress the amplification in the torsional vibration, a continuously sliding friction mechanism (often called as a hysteresis mechanism) which continuously slides through the entire range of the engine speeds is disposed between the driving and driven side flywheels.
However, there are two problems with the above-described prior art flywheels. One problem is that a considerably large resonance remains at the resonance speed even if the friction mechanism is provided, because the characteristic of the flywheel is determined more by the spring mechanism than by the friction mechanism. The other problem is that the friction mechanism deteriorates the acceleration transmittance rate (which corresponds to a damping characteristic of the flywheel) in the standard range of engine speeds above the idling speed. This is because the frictional force due to the sliding friction mechanism exists over the entire range of engine speeds and because temporary sticking frequently occurs in the friction mechanism.
Another U.S. Application, Ser. No. 07/93,573 filed Sept. 4, 1987 relates to a flywheel designed to overcome the deficiencies of the above-described flywheel structure. However, as will become more apparent below, that application presents a structurally different, other solution to the problems of the prior art flywheel than the present invention.